I have a question regarding the design decision for Istio’s current circuit breaking strategy.
As far as I can see in the docs, the concrete circuit breaking behavior can be expressed as trafficPolicy inside the DestinationRule resource. This implies that properties such as maxConnections are expressed at the server-side (the destination). However, in most library-based white box approaches such as Netflix the conditions for opening the breaker are expressed on the client-side. On one hand the consequence of this strategy is that it is not possible (with Istio) to specify conditions specific to a specific client consuming the service. On the other hand, it is possible to reason on maxConnections from the service’s point of view with the server-side strategy.
The pattern described above does not only apply for circuit breaking but also for timeouts for example which are expressed in the virtual service (again server/service-side).
Based on those observations, would it make sense to extend Istio to express properties or constraints not only for destinations (DestinationRule) but also for sources (SourceRule?) or even a more powerful ruleset where I could have selectors based on destination AND source? What do you think?